Abstract. Dynamics of a non-linear energy harvesting is affected by excitation source and to explore efficiency it is necessary to understand which region offers more energy and the influence of a forced periodic vibration related to ambient non-ideal and power source. A bistable Duffing oscillator coupled to piezoelectric layers and electric load configuring a non-linear energy harvesting is excited by periodic resonant vibration and the system behaviour and energy availability is compared to non-ideal excitation. The chaos via Lyapunov exponent were determined and Runge-Kutta forth order was applied to determine displacement, velocity, phase portrait and output voltage. As main conclusion it was possible to identify a more efficient coupling of cantilever configuration to non-ideal power source than resonant periodic excitation. Considering the kinetic energy available for the coupled system to be converted into electricity it was possible to verify an increase around then times of energy offered to the harvesting system from non-ideal vibration compared to periodic resonant design.